The rate of uninsured Americans dropped slightly in 2012, from 15.7 percent to 15.4 percent, the U.S. Census Bureau reported Tuesday.

The closely-watched report found that more than 48 million Americans were uninsured during 2012, down from 48.6 million in 2011, a change the agency said is not statistically significant.

"It is encouraging that fewer people were uninsured in 2012 than in the previous year, but the huge number of Americans still without health insurance is a stark reminder of the important work that lies ahead," Ron Pollack, executive director of Families USA, a consumer advocacy group, said in a statement.

The major provisions of the Affordable Care Act designed to expand coverage will take effect Jan. 1, 2014.

One of the most significant changes was a decline in the rate of uninsured children, from 9.4 percent in 2011 to 8.9 percent, largely related to government efforts to make it easier for children to get coverage.

"Uninsurance is already low for children, and the fact that it still appears to be declining is an encouraging sign and shows when there is a concerted public policy focus on a problem it can pay off," said Genevieve Kenney, a senior fellow at the Urban Institute.

Kenney said more kids were being covered under their parents’ workplace policies. In addition, states and the federal government have made it easier to enroll in Medicaid and the Children’s Health Insurance Program and stay enrolled.

"This is the most positive news there is on uninsurance," in the report, she said. "For other age groups we did not see increases in uninsured, but we did not see drops either."

The uninsured rates for all other age groups showed no statistically significant change, the bureau reported.

In 2012, the percentage of people covered by private health insurance continued to hover at 63.9 percent , with 54.9 percent covered through their employers.

And while the percentage of those enrolled in Medicaid, the state-federal program for the poor, remained about the same, the percentage of those covered by Medicare rose from 15.2 percent in 2011 to 15.7 percent in 2012.

Kaiser Health News is an editorially independent program of the Henry J. Kaiser Family Foundation, a nonprofit, nonpartisan health policy research and communications organization not affiliated with Kaiser Permanente.

Copyright 2013 The Associated Press. All rights reserved. This material may not be published, broadcast, rewritten or redistributed.